This invention relates to surgical staples, and more particularly to surgical staples of the type which are formed around an anvil in a surgical stapler.
Surgical stapling apparatus for applying staples to close incisions or wounds in body tissue are shown, for example, in Green et al. U.S. Pat. Nos. 3,643,851, Smith 3,650,453, and Green 3,837,555. In these devices, a surgical staple which is typically preformed in a broad-based, square-cornered U shape is advanced toward an anvil by a staple pusher having an end with a generally U-shaped recess. The base of the U-shaped recess in the staple pusher is broader than the anvil, but not as broad as the base of the U-shaped staple. When the staple reaches the anvil, the staple pusher causes the staple to bend around the anvil into a closed, square-cornered C shape. (In this specification and in the appended claims, this is referred to as forming the staple.) As this is taking place, the ends of the staple enter the tissue on the respective opposite sides of the incision or wound and draw the tissue together. When the staple has been fully formed, the staple pusher is retracted and the stapler is removed by sliding the anvil out from within the staple. The staple remains in the tissue to hold it together during healing.
Occasionally in surgical staplers of the type described above, the staple may not readily release from the U-shaped recess in the staple pusher after the staple has been formed and the staple pusher is being retracted. This may be because of residual stresses in the staple which cause it to press against the sides of the staple pusher recess in a spring-like fashion. When this occurs, the formed staple tends to be pulled back into the stapler, with the possible consequences of injury to the tissue being stapled and difficulty in freeing the stapler from the staple.
One solution which has been found to this occasional problem is to design the stapler so that the fit between the staple pusher, the staple, and the anvil is relatively loose, with the degree of looseness being carefully selected and controlled to minimize the instances in which the staple pusher fails to readily release the staple. Achieving and maintaining just the right degree of looseness in the design of the stapler, however, requires extremely precise manufacturing tolerances, thereby increasing the cost of the stapler. This relatively loose design may also produce finished staples which are not as neatly and regularly formed as would be most desirable. It may also contribute to other possible operating problems in the stapler, such as allowing a staple to occasionally roll, twist, or slip off the anvil during formation, with the result that the staple is improperly or incompletely formed or not formed at all. These problems of rolling, twisting, and slipping are most likely to occur with staples made of round wire, which is the most common and generally the preferred surgical staple stock.
In view of the foregoing, it is an object of this invention to provide improved surgical staples of the type which are formed by being bent around an anvil.
It is a more particular object of this invention to provide improved surgical staples of this type which are not subject to being pulled back into the stapler when the staple pusher is retracted, and which may also have reduced tendency to roll, twist, or slip off the anvil during formation.